This is related to how the server is characterizing the content in the Response Headers:

Image 3: Content-Type: image/jpeg

Image 4: Content-Type: image/jpeg

Image 5: Content-Type: application/octet-stream

Is this the Upgit you're using: https://github.com/pluveto/upgit

Based on a very cursory search of the source, it seems to base the Content-Type on the mimeType determined from the file extension, with application/octet-stream as the fallback. I didn't spend enough time on it to know where the problem is.

Is this the Upgit you're using: https://github.com/pluveto/upgit

Yes.

Based on a very cursory search of the source, it seems to base the Content-Type on the mimeType determined from the file extension, with application/octet-stream as the fallback. I didn't spend enough time on it to know where the problem is.

I'm not sure why that would happen as they are all the same file extension and file format (.jpg/.jpeg). I've tested this out more in the last 30 minutes or so and I'm able to reproduce if the files uploaded are above about 5MiB or so (I haven't determined the exact size), then I get prompted to download the image instead of the image displaying. It doesn't matter what image format I upload nor file extension. I've tried PNG/WebP/JPEG/JPG and I'm pretty confident there is a threshold where if the file size is above a certain amount you get the prompt.

Do you know more about why a larger image file would be handled as application/octet-stream rather than it's proper mimeType?

Thanks for any further information.

Edit: I seem to recall a setting in about:config that controls a delay period for determining the content type of a resource, but I can't remember what it is. I did a bit of tweaking in about:config when I first set up firefox and I'm wondering if a setting I changed is causing this. Can you confirm that you're getting the same behavior on a firefox profile without any about:config changes?

For some reason the response I just posted to your reply got deleted - not sure why.

This is related to how the server is characterizing the content in the Response Headers: Is this the Upgit you're using: https://github.com/pluveto/upgit

Yes, that's the app.

Based on a very cursory search of the source, it seems to base the Content-Type on the mimeType determined from the file extension, with application/octet-stream as the fallback. I didn't spend enough time on it to know where the problem is.

I've been able to reproduce the issue with all sorts of different image files and the common denominator is file size. It appears any image file above ~5MiB or so (I don't know the exact size) causes this to happen. I've tried JPG/JPEG/PNG/WEBP images and they all elicit the same behavior if their file size is large.

Regarding the mimeType being determined from the file extension - that doesn't seem to align with what I'm seeing as I test this. It happens with all different file extensions. Do you know why the fallback to application/octet-stream would occur?

Thanks for any further help.

I'm assuming this is on Github's side, but I can't seem to find any documentation. Maybe the developer of Upgit has some insight into it.